TU Darmstadt, Darmstadt, Germany
DESY, Hamburg, Germany
Uni HH, Hamburg, Germany
TEMF, TU Darmstadt, Darmstadt, Germany
The Free Electron Laser in Hamburg (FLASH) is currently equipped with four Bunch Arrival time Monitors (BAM’s) which are part of the optical synchronization system [1-2]. FLASH usually works with bunch charges of 0.2 to 1 nC, but for a variety of future experiments, the system needs to operate with bunch charges in the range of 10 to 20 pC. Below 0.2 nC the sensitivity of such a BAM scales approximately linearly with the bunch charge and therefore the system no longer fulfills the time resolution requirements for these low charges. For the low bunch charge regime operation, the bandwidth has to be increased substantially. This paper shows a new design of a high frequency button pickup that can operate in a frequency band from DC up to 40 GHz. The design criteria of the pickup are the voltage slope steepness at the zero-crossing, the maximum amplitude and the ringing of the picked-up voltage. The performance of the designed model is analyzed for fabrication tolerances and orbit variations. Some manufacturing and practical issues are discussed and solutions are offered for improving the results. A full wave simulation with CST PARTICLE STUDIO is performed in order to prove the concept.
[1] F. Loehl et. al.,“A Sub 100 fs Electron Bunch Arrival-time Monitor System for FLASH”, THOBFI01, EPAC 2006
[2] F. Loehl et. al.,“A Sub-50 Femtosecond bunch arrival time monitor system for FLASH”, WEPB15, DIPAC 2007
TU Darmstadt, Darmstadt, Germany
DESY, Hamburg, Germany
Uni HH, Hamburg, Germany
TEMF, TU Darmstadt, Darmstadt, Germany
The Free Electron Laser in Hamburg (FLASH) is equipped with Bunch Arrival time Monitors (BAM)[1], which provide for a time resolution of less than 10 fs for bunch charges higher than 0.2 nC. Future experiments, however, will aim at generating FEL light pulses from bunch charges of 10-20 pC. The sensitivity of the measurement system is defined by the slope of the pickup signal at the zero crossing and scales close to linear with the bunch charge. The requirements on the time resolution will no longer be fulfilled when operating at decreased bunch charges. Several designs have been developed in CST PARTICLE STUDIO®, each having an increased bandwidth larger than 40 GHz for meeting the requirements when operating at low bunch charges. Furthermore, new post-processing functions for the automatic evaluation of the signal slope and the ringing in the detected voltage signal have been developed and implemented within the CST software for defining optimization goals of the built-in optimizer for determining free design parameters. Results of the new designs are presented and compared with the current BAM pickup.
[1] M.K. Bock et.al., "Recent Developments of the Beam Arrival Time Monitor with Femtosecond Resolution at FLASH", WEOCMH02, IPAC 2010